diff --git a/library/include/mobilisis/calculate_price.h b/library/include/mobilisis/calculate_price.h
index 18fa959..6a6040e 100644
--- a/library/include/mobilisis/calculate_price.h
+++ b/library/include/mobilisis/calculate_price.h
@@ -197,11 +197,11 @@ int CALCULATE_LIBRARY_API compute_next_timestep(parking_tariff_t *tariff, int cu
 
 QList<int> CALCULATE_LIBRARY_API get_time_steps(Configuration *cfg);
 
-int CALCULATE_LIBRARY_API get_minimal_parkingtime(Configuration *cfg,
+int CALCULATE_LIBRARY_API get_minimal_parkingtime(Configuration const *cfg,
                                                   PERMIT_TYPE permitType = PERMIT_TYPE::SHORT_TERM_PARKING,
                                                   int paymentOptionIndex=0);
 
-int CALCULATE_LIBRARY_API get_maximal_parkingtime(Configuration *cfg,
+int CALCULATE_LIBRARY_API get_maximal_parkingtime(Configuration const *cfg,
                                                   PERMIT_TYPE permitType = PERMIT_TYPE::SHORT_TERM_PARKING,
                                                   int paymentOptionIndex=0);